A class of thermoelastic sulfonated polymer has been described in a number of U.S. patents, wherein these sulfonated elastomeric polymer have been produced from commercial elastomeric polymers by either sulfonating with a sulfur trioxide complexed with Lewis base or an acetyl sulfate.
These previous patents teach a batch method of sulfonation which comprises reacting the elastomeric polymer with the sulfonating agent in a reaction vessel to form an unneutralized sulfonated polymer and then adding a neutralizing agent to the reaction vessel to neutralize the unneutralized sulfonate polymer.
U.S. Pat. No. 3,642,728, herein incorporated by reference, clearly teaches a method of selective sulfonation of olefinic unsaturation sites of an elastomeric polymer such as Vistalon 3509 having a Mooney viscosity of 90 at 100.degree. C. to form an acid form of a sulfonated elastomeric polymer. The olefinic sites of the elastomeric polymer are sulfonated by means of a sulfur trioxide complexed with a Lewis base. The SO.sub.3 H groups of the sulfonated elastomer are directly neutralized in the reaction vessel with a basic material to form an ionically cross-linked elastomer having substantially improved physical properties over an unsulfonated elastomer at room temperature.
U.S. Pat. Nos. 3,836,511 and 4,184,988, herein incorporated by reference, teach a batch process for the sulfonation of the olefinic sites of the elastomeric polymer, wherein the sulfonating agent is selected from acetyl sulfate, propionyl sulfate and butyryl sulfate. The neutralizing agents employed to neutralize the unneutralized form of the sulfonated elastomeric polymers are organic amines or inorganic bases.
Again the neutralizing agent is added directly to the reaction vessel containing the unneutralized sulfonated polymer to form the neutralized sulfonated polymer.
The continuous process for sulfonation of elastomeric polymers as described in this invention provides a means for employing stoichiometric amounts of sulfonation and neutralization agents thereby permitting reduction in co-solvent requirements to less than 4 vol. % and to maintain neutralized cement viscosities below 25,000 c.P. at 20 wt.% polymer solid concentration level.
The instant process can be generally described as an improved, in-line continuous process for the sulfonation and subsequent neutralization of elastomeric polymers. The dissolved polymer cement is continuously contacted in a well-stirred, staged reactor with a sulfonating agent which can be preformed and continuously fed in the reactor or formed, in situ, in the reactor. Stoichiometric sulfonation is achieved in residence times of about 1 to about 20 minutes; more preferably less than about 10 minutes. The sulfonated cement is continuously terminated and neutralized in a separate, staged neutralization vessel at residence times of about 1 to about 20 minutes. The sulfonated and neutralized cement is then steam stripped and the neutralized sulfonated elastomeric polymer is isolated as a crumb or powder which can be dried and finished in a hot-air dryer.